Add a missing file

Issue #98

Prepare 1.8

Prepare 1.7

Prepare 1.6

Bump up version number to 1.5.1

Update README.md

Fix Makefile to install pg_ivm--1.3--1.4.sql (#45)

This should have be included in the previous commit but was
accidentally forgotten. Issue #43

Bump up version number to 1.4

Merge branch 'main' of https://github.com/sraoss/pg_ivm into main

Merge branch 'main' of https://github.com/sraoss/pg_ivm into main